A process for the anionic polymerization of caprolactam to produce fine denier polyamide 6 fibers

Abstract

The present application relates to a kind of anionic polymerization preparation polyamide 6 fine denier fiber method.Caprolactam, catalyst are added to dry device A to remove system moisture after being placed in storage tank A, caprolactam is added to dry device B to remove moisture after being placed with initiator, cyclic oligomer inhibitor in storage tank B, then the caprolactam liquid in storage tank A and storage tank B is continuously injected into screw extruder to carry out anionic ring-opening polymerization reaction and prepare polyamide 6 base melt, further the base melt is transported to the removal of monomer and part of cyclic oligomer in series devolatilization reaction system, obtain polyamide 6 final polymer, finally can directly carry out spinning, obtain polyamide 6 fine denier fiber.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fiber manufacturing, and particularly relates to a method for preparing fine denier polyamide 6 fiber by anionic polymerization. BACKGROUND

[0002] Polyamide 6 (PA6) fiber is widely used in clothing, home textiles and industrial fields due to its excellent mechanical properties, wear resistance and chemical stability. Fine denier fiber has soft touch, delicate luster and high coverage, and is the closest fiber to human skin. The preparation of fine denier fiber has high requirements for the quality of the fiber-forming polymer, and the content of residual small molecules in the system is also required to be high.

[0003] In the conventional production of polyamide 6, when the polymer reaches equilibrium, the conversion rate of caprolactam is generally about 90%, and about 10% of residual caprolactam monomer and cyclic oligomer small molecules (also known as hot water extractables) need to be removed by a hot water continuous extraction process for tens of hours, which consumes a large amount of energy and water resources. Anionic polymerization for preparing polyamide 6 has the advantages of fast and efficient reaction, low pollution and low energy consumption, but there are still many problems in the existing technology, such as the need to remove residual monomers and oligomers to meet the requirements of fiber processing.

[0004] A small amount of monomers and oligomers can be removed by vacuum devolatilization. Hyoungsan Kye et al. (Journal of Applied Polymer Science 1994, 52(9), 1249-1262) used vacuum devolatilization to remove monomers and oligomers from anionic polyamide 6, and then added a spinneret at the outlet of a screw extruder for direct melt spinning. However, due to the presence of a large amount of oligomers, the fiber produced is in millimeter scale, which does not meet the requirements of daily use of fiber. Efficient removal of residual monomers and oligomers from anionic polymerization polyamide 6 is expected to shorten the production time, reduce the production energy consumption, and promote the green and low-carbon development of the polyamide 6 material industry. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing fine denier polyamide 6 fiber by anionic polymerization, which uses a cyclic oligomer inhibitor to reduce the production of monomers and cyclic oligomers during polymerization, and removes the monomers and oligomers by using a series devolatilization reactor, so that the obtained polyamide 6 melt can be directly spun to obtain fine denier polyamide 6 fiber.

[0006] The introduction of a cyclic oligomer inhibitor in the anionic polymerization process of polyamide 6 has the following effects:

[0007] In one aspect, the metal ions in the cyclic oligomer inhibitor coordinate with the amide bonds of polyamide 6, preventing the amide bonds from being attacked by cyclization during polymerization, reducing the formation of cyclic oligomers, and thus reducing the content of cyclic oligomers in the polymer.

[0008] In another aspect, the anionic polymerization of polyamide 6 is usually very fast, releasing a large amount of polymerization heat in a short time, causing the system temperature to rise, and increasing the content of monomers and cyclic oligomers and other small molecules. The cyclic oligomer inhibitor added in the present application can appropriately reduce the reaction rate, making the entire anionic polymerization system more moderate and controllable, and controlling the content of small molecules.

[0009] Caprolactam monomers account for the vast majority of small molecules remaining in polyamide 6. Although caprolactam has a low boiling point and is easy to remove by devolatilization, the difficulty of removing cyclic oligomers at the same time is increased, and the accumulation of cyclic oligomers (especially cyclic dimers) can affect the product quality of the polyamide 6 processing stabilizer. Based on the differences in the physical properties of caprolactam monomers and cyclic oligomers in polyamide 6 and the relationship between the temperature and pressure of the devolatilization reactor, the present application proposes a series devolatilization reaction system using a first devolatilization reactor and a second devolatilization reactor in series. Since caprolactam monomers have a lower boiling point, the reaction temperature of the first devolatilization reactor of the series devolatilization reaction system is set to 240-280°C, and the reaction pressure is 200-4000 Pa. This condition can selectively remove more than 90% of the caprolactam monomers, reducing the energy consumption required for vacuum power while effectively reducing the impact of high levels of monomers on the next devolatilization reaction. After a large amount of caprolactam monomers are removed, the present application sets the reaction temperature of the second devolatilization reactor of the series devolatilization reaction system to 240-280°C and the reaction pressure to 20-600 Pa based on the physical parameters of the cyclic oligomers, which can achieve enhanced removal of the remaining small amount of caprolactam monomers and cyclic oligomers, achieving a monomer residue of less than 0.1wt% in the final polymer, a cyclic oligomer content of less than 1.2wt% (of which the cyclic dimer content in the cyclic oligomer is less than 0.1wt%), and a hot water extractable content of less than 0.4wt%. This method omits the steps of cooling, granulating, hot water extraction, drying, and remelting compared to the traditional hot water extraction method, saving a large amount of time and energy.

[0010] Based on the above series devolatilization reaction system, the present technical solution provides a method for preparing polyamide 6 fine denier fibers by anionic polymerization, comprising the following steps:

[0011] (1) Prepare a basic active material A: uniformly mix the catalyst with caprolactam to obtain a first mixture, and store the first mixture in a storage tank A after vacuum distillation, wherein the storage tank A is protected by an inert atmosphere and the temperature is constant at 80-150°C;

[0012] (2) Preparing base active material B: heating and melting caprolactam, then performing vacuum distillation, mixing the caprolactam with removed water with an initiator and a cyclic oligomer inhibitor to obtain a second mixture, and storing the second mixture in a storage tank B, wherein the storage tank B is protected by an inert atmosphere and has a constant temperature of 80-150°C;

[0013] (3) Injecting the base active materials A and B into a screw extruder in a volume ratio of 1-10:10 to perform anionic polymerization, and reacting and extruding to obtain a polyamide 6 base melt;

[0014] (4) Transporting the polyamide 6 base melt to a first devolatilization reactor to remove caprolactam monomers to obtain a polyamide 6 intermediate, and transporting the polyamide 6 intermediate to a second devolatilization reactor to remove a small amount of caprolactam monomers, cyclic dimers, part of cyclic trimers, and part of cyclic tetramers to obtain a polyamide 6 final polymer, wherein the reaction temperature of the first devolatilization reactor is set to 240-280°C, and the reaction pressure is 200-4000 Pa, and the reaction temperature of the second devolatilization reactor is 240-280°C, and the reaction pressure is 20-600 Pa;

[0015] (5) Transporting the polyamide 6 final polymer to a spinning machine to directly perform spinning to obtain a polyamide 6 fine denier fiber.

[0016] In some embodiments, in (1), the catalyst is one or more of sodium caprolactamate, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, and KOH.

[0017] In step (1), the inert atmosphere is one or more of N2, CO2, He, Ne, and Ar.

[0018] In step (1), 0.3-1.2 parts by mass of the catalyst and 10-100 parts by mass of caprolactam are mixed to obtain a first mixture.

[0019] In step (1), the first mixture is subjected to vacuum distillation to sufficiently remove water, and the vacuum distillation is performed at a temperature of 80-150°C and a reaction absolute pressure of 5-95 kPa.

[0020] In step (2), the initiator is one or more of N-acetyl caprolactam (AcCL), bisacylated lactam-1,6-hexanediol, terephthaloyl bis-caprolactam (TBCL), isophthaloyl bis-caprolactam, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and 1,6-hexane diisocyanate (HMDI).

[0021] Similarly, in step (2), the caprolactam is subjected to vacuum distillation to remove water, and the vacuum distillation is performed at a temperature of 80-150°C and an absolute pressure of 5-95 kPa.

[0022] In step (2), the inert atmosphere is one or more of N2, CO2, He, Ne, and Ar.

[0023] In step (2), 100 parts of caprolactam, 1.0-2.4 parts of an initiator, and 0.01-2.0 parts of a cyclic oligomer inhibitor are mixed in a mass ratio to obtain a second mixture.

[0024] In step (2), the cyclic oligomer inhibitor is one metal ion compound MY or a mixture of two or more metal ion compounds MY, wherein M is a metal cation and Y is an inorganic anion or an organic anion.

[0025] Specifically, the metal cation M is selected from one of a transition metal ion, a lanthanide metal ion, and a Group IIA metal ion. When the metal cation M is selected from a transition metal ion, the metal cation M is Sc 3+ , Ni 2+ , Zn 2+ , Y 3+ , Zr 4+ , Ru 4+ , Rh 3+ ; when the metal cation M is selected from a lanthanide metal ion, the lanthanide metal ion is La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Lu 3+ , Yb 3+ ; and when the metal cation M is selected from a Group IIA metal ion, the Group IIA metal ion is one of Be 2+ , Mg 2+ , Ca 2+ ; and the metal cation M can also be one of Li + , Al 3+ .

[0026] The inorganic anion or organic anion Y is selected from F - , Cl - , NO3 - , SO4 2-PO4 3- , citrate ion, salicylate ion, 3-hydroxybutyrate ion, L-aspartate ion, lactate ion, malate ion, one of 2-hydroxypropionate ion, organic monobasic acid ion H(CH2) n COO - (n = 0 ~ 12), benzoate ion, naphthoate ion, organic dibasic acid ion COO - (CH2) m COO - (m = 0 ~ 12), terephthalate ion, phthalate ion, isophthalate ion or naphthalate ion, saturated fatty acid ion C x H 2x+1 COO - (x = 13 ~ 20), unsaturated fatty acid ion, 6-aminohexanoate ion NH2C5H 10 COO - , one of the amino acid ions. When the inorganic anion or organic anion is an unsaturated fatty acid ion, the unsaturated fatty acid ion is oleate ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenate ion C 17 H 29 COO - , arachidonate ion C 19 H 31 COO - , palmitoleate ion C 15 H 29 COO - ; when the inorganic anion or organic anion is an amino acid ion, the amino acid ion is any one of glycine ion, alanine ion, valine ion, leucine ion, isoleucine ion, proline ion, phenylalanine ion, methionine ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteine ion, tyrosine ion, selenocysteine ion.

[0027] In some embodiments, the amount of the cyclic oligomer inhibitor added is 0.01 wt% to 2.0 wt% of the caprolactam.

[0028] In step (3), the screw extruder is set to a feeding temperature of 90-160 ℃, a discharge port temperature of 220-240 ℃, and a screw intermediate section temperature gradually increasing from the feeding temperature to the discharge port temperature, with at least one heating section, and a rotation speed of 20-300 rpm.

[0029] In step (3), the polyamide 6 base melt has a relative viscosity of 2.0-3.5, a monomer content of less than 3.9 wt%, a cyclic oligomer content of less than 2.0 wt%, a hot water extractable content of less than 4.6 wt%, and a cyclic dimer content in the cyclic oligomers of less than 0.5 wt%.

[0030] In step (4), the reaction temperatures of the first and second devolatilization reactors are independently controllable and are connected to a vacuum system for controlling the reaction pressures of the first and second devolatilization reactors, wherein the first devolatilization reactor is selected from one of a horizontal squirrel cage reactor, a horizontal disc reactor, a falling bar devolatilizer, and a vertical falling film devolatilization reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor or a horizontal double-shaft devolatilization reactor; the reaction pressure of the first devolatilization reactor is controlled by the vacuum system to be 200-4000 Pa, and the reaction temperature is set to 240-280 °C; the reaction pressure of the second devolatilization reactor is controlled by the vacuum system to be 20-600 Pa, and the reaction temperature is set to 240-280 °C.

[0031] In step (4), the polyamide 6 final polymer has a relative viscosity of 2.0-3.5, a monomer content of less than 0.1 wt%, a cyclic oligomer content of less than 1.2 wt%, a cyclic dimer content in the cyclic oligomers of less than 0.1 wt%, and a hot water extractable content of less than 0.4 wt%.

[0032] The polyamide 6 final polymer obtained by the above method can be directly spun into polyamide 6 fine denier fibers at a spinning temperature of 245-300 °C and a spinning speed of 2500-6000 m / min.

[0033] Figure 1 、 Figure 2 and Figure 3 Three schematic diagrams of the above methods for preparing polyamide 6 fine denier fibers by anionic polymerization are provided as follows: Figure 1 、 Figure 2 and Figure 3As shown, the caprolactam and the catalyst are mixed and then added to the drying device A for vacuum distillation and stored in the storage tank A, the caprolactam is heated and melted and then placed in the drying device B for vacuum distillation, the caprolactam with removed water is mixed with the initiator and the cyclic oligomer inhibitor to obtain a second mixture, the second mixture is stored in the storage tank B; the base active material A and the base active material B are injected into the screw extruder at a volume ratio of 1-10:10 for anionic polymerization, and a polyamide 6 base melt is prepared by reaction extrusion; the polyamide 6 base melt is transported to the devolatilization reactor 1 for selectively removing more than 90% of the caprolactam monomer, and after the caprolactam monomer is largely removed, it enters the devolatilization reactor 2 for enhanced removal of the residual small amount of caprolactam monomer and cyclic oligomer to obtain a polyamide 6 final polymer. Figure 1 The devolatilization reactor 1 in the above method adopts a vertical falling film devolatilization reactor, and the devolatilization reactor 2 also adopts a vertical falling film devolatilization reactor; Figure 2 The devolatilization reactor 1 in the above method adopts a horizontal devolatilization reactor, and the devolatilization reactor 2 adopts a vertical falling film devolatilization reactor, Figure 3 The devolatilization reactor 1 in the above method adopts a horizontal devolatilization reactor, and the devolatilization reactor 2 adopts a horizontal double-shaft devolatilization reactor.

[0034] The technical scheme of the present application can achieve the following beneficial effects:

[0035] (1) In the process of anionic polymerization of polyamide 6, the cyclic oligomer inhibitor is introduced, the metal ions in the cyclic oligomer inhibitor are coordinated with the amide bond of polyamide 6, the amide bond is prevented from being attacked and cyclized during polymerization, the formation of cyclic oligomers is reduced, and the content of difficult-to-devolatilize cyclic oligomers in the polymer is reduced.

[0036] (2) According to the physical property differences of the monomer and the cyclic oligomer, the reaction temperature and pressure of the devolatilization reactor are controlled respectively, more than 90% of the caprolactam monomer can be selectively removed in the first devolatilization reactor, and the influence of high content of monomer on the next devolatilization reaction is effectively reduced. After the monomer is largely removed, the reaction temperature and pressure of the second devolatilization reactor are set according to the physical properties of the cyclic oligomer, and the residual small amount of caprolactam monomer and cyclic oligomer can be enhanced and removed. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.0-3.5, a monomer content of less than 0.1wt%, a cyclic oligomer content of less than 1.2wt% (of which the cyclic dimer content is less than 0.1%), and a hot water extract content of less than 0.4wt% is prepared, so as to prepare polyamide 6 fine denier fibers. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 、 Figure 2 and Figure 3The schematic diagram of the anionic polymerization preparation of the polyamide 6 fine fiber is shown in the application. DETAILED DESCRIPTION

[0038] The application will be further described in conjunction with the specific embodiments. It should be understood that these embodiments are only used for illustrating but not for limiting the scope of the application. Furthermore, it should be understood that after reading the content taught by the application, those skilled in the art can make various alterations or modifications to the application, and these equivalent forms also fall within the scope defined by the appended claims of the application.

[0039] In order to further illustrate the application, the anionic polymerization preparation of the high-quality polyamide 6 fiber provided by the application is described in detail in conjunction with the embodiments, but they should not be understood as limiting the scope of the protection of the application.

[0040] The application measures the content of the monomer and the cyclic oligomer in the polyamide 6 base melt and the final polymer by using the ultra-high performance liquid chromatograph, and the specific condition parameters are as follows:

[0041] The chromatographic column is T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or the equivalent;

[0042] The column temperature is 30℃;

[0043] The flow rate is 0.3 mL / min;

[0044] The detection wavelength is 200 nm;

[0045] The sample injection amount is 2 μL;

[0046] The elution program (as shown in the following table) is that the mobile phase A is water and the mobile phase B is acetonitrile.

[0047]

[0048] Comparative example

[0049] The method for preparing the polyamide 6 fine fiber by anionic polymerization comprises the following specific steps:

[0050] (1) Preparation of the base active material A: 0.8 parts of NaOH is added into 100 parts of caprolactam by mass fraction, and then mixed uniformly, and the water is removed by distillation under reduced pressure at 120℃ and 5kPa, and then stored in the storage tank A with Ar protection and constant temperature of 120℃;

[0051] (2) Preparation of base active material B: 100 parts of monomer caprolactam were heated and melted, and water was removed by distillation under reduced pressure at 120°C and 5kPa, then 1.5 parts of N-acetyl caprolactam was added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 120°C;

[0052] (3) The base active materials A and B were injected into the screw extruder in a volume ratio of 1:1 for anionic polymerization, the screw extruder feed temperature was set to 100°C, the screw extruder discharge temperature was set to 230°C, the screw intermediate segment temperature was set to gradually increase from 100°C to 230°C, the heating section was 2, the speed was 30 rpm, and a polyamide 6 melt with a relative viscosity of 2.81, a monomer content of 4.13wt%, a cyclic oligomer content of 2.49wt% (including a cyclic dimer content of 0.75wt%), and a hot water extractable content of 5.35wt% was prepared by reaction extrusion;

[0053] (4) The polyamide 6 melt was transported to a spinning machine for direct spinning, the spinning temperature was 270°C, and the winding speed was 4200m / min. A large amount of caprolactam volatile gas was generated during polyamide 6 spinning, and fibers could not be formed.

[0054] Example 1

[0055] A method for preparing polyamide 6 fine denier fibers by anionic polymerization, the specific steps are as follows:

[0056] (1) Preparation of base active material A: 0.8 parts of NaOH was added to 100 parts of caprolactam and mixed uniformly, and then stored in a storage tank A under Ar protection and at a constant temperature of 120°C;

[0057] (2) Preparation of base active material B: 100 parts of monomer caprolactam were heated and melted, and water was removed by distillation under reduced pressure at 120°C and 5kPa, then 1.5 parts of N-acetyl caprolactam and 1.5 parts of magnesium chloride were added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 120°C;

[0058] (3) The base active materials A and B were injected into the screw extruder in a volume ratio of 1:1 for anionic polymerization, the screw extruder feed temperature was set to 100°C, the screw extruder discharge temperature was set to 230°C, the screw intermediate segment temperature was set to gradually increase from 100°C to 230°C, the heating section was 2, the speed was 30 rpm, and a polyamide 6 melt with a relative viscosity of 2.80, a monomer content of 3.41wt%, a cyclic oligomer content of 1.49wt% (including a cyclic dimer content of 0.39wt%), and a hot water extractable content of 3.82wt% was prepared by reaction extrusion.

[0059] (4) The above base melt is transported through a pipeline to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a horizontal squirrel-cage reactor, and the second devolatilization reactor is a vertical falling-film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum system. The temperature of the first devolatilization reactor is 240 °C, and the reaction pressure is 1000 Pa. The temperature of the second devolatilization reactor is 270 °C, and the reaction pressure is 60 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.81, a monomer content of 0.01wt%, a cyclic oligomer content of 0.69wt% (of which the cyclic dimer content is 0.07wt%), and a hot water extractable content of 0.26wt% is obtained;

[0060] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 270 °C, and the winding speed is 4200m / min. A high-quality polyamide 6 fine denier fiber is obtained, the fiber specification is 50D / 136F, the fiber breaking strength is 5.2cN / dtex, and the elongation is 23%.

[0061] Example 2

[0062] A method for preparing a polyamide 6 fine denier fiber by anionic polymerization, the specific steps are as follows:

[0063] (1) Preparation of base active material A: 1.0 parts of NaOH is added to 10 parts of caprolactam and mixed uniformly, then distilled to remove water at 120 °C and 50 kPa under reduced pressure, and then stored in a storage tank A under N2 protection and at a constant temperature of 130 °C;

[0064] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, then distilled to remove water at 120 °C and 50 kPa under reduced pressure, then 1.3 parts of terephthaloyl bis-caprolactam (TBCL) and 1.5 parts of zinc citrate are added and mixed uniformly, and then stored in a storage tank B under N2 protection and at a constant temperature of 130 °C;

[0065] (3) The base active materials A and B are injected into a screw extruder at a volume ratio of 1:10 for anionic polymerization, the feeding temperature of the screw extruder is set to 120 °C, the discharging temperature of the screw extruder is set to 220 °C, the intermediate temperature of the screw is set to gradually increase from 120 °C to 220 °C, there are three heating sections, and the rotation speed is 40 rpm. A polyamide 6 base melt with a relative viscosity of 3.30, a monomer content of 3.76wt%, a cyclic oligomer content of 1.52wt% (of which the cyclic dimer content is 0.41wt%), and a hot water extractable content of 3.84wt% is prepared by reaction extrusion;

[0066] (4) The above base melt is transported through a pipeline to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a horizontal disc reactor, and the second devolatilization reactor is a vertical falling-film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum system. The temperature of the first devolatilization reactor is 260 °C, and the reaction pressure is 2500 Pa. The temperature of the second devolatilization reactor is 250 °C, and the reaction pressure is 60 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 3.31, a monomer content of 0.02wt%, a cyclic oligomer content of 0.57wt% (of which the cyclic dimer content is 0.08wt%), and a hot water extractable content of 0.29wt% is obtained;

[0067] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 275 °C, and the winding speed is 3000 m / min. A high-quality polyamide 6 fine denier fiber is obtained, the fiber specification is 50D / 96F, the fiber breaking strength is 7.2 cN / dtex, and the elongation is 20%.

[0068] Example 3

[0069] A method for preparing a polyamide 6 fine denier fiber by anionic polymerization, the specific steps are as follows:

[0070] (1) Preparation of base active material A: 0.5 parts of sodium ethoxide is added to 100 parts of caprolactam and mixed uniformly, then distilled to remove water at 100 °C and 20 kPa under reduced pressure, and then stored in a storage tank A under Ar protection and at a constant temperature of 100 °C;

[0071] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, then distilled to remove water at 100 °C and 20 kPa under reduced pressure, then 0.5 parts of terephthaloyl bis-caprolactam (TBCL) and 1.1 parts of magnesium chloride are added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 100 °C;

[0072] (3) The base active materials A and B are injected into a screw extruder at a volume ratio of 1:1 for anionic polymerization, the feeding temperature of the screw extruder is set to 150 °C, the discharging temperature of the screw extruder is set to 230 °C, the intermediate temperature of the screw is set to gradually increase from 150 °C to 230 °C, there are three heating sections, and the rotation speed is 40 rpm. A polyamide 6 base melt with a relative viscosity of 2.40, a monomer content of 3.47wt%, a cyclic oligomer content of 1.33wt% (of which the cyclic dimer content is 0.42wt%), and a hot water extractable content of 3.76wt% is prepared by reaction extrusion;

[0073] (4) The above base melt is transported through a pipeline to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a falling strip devolatilizer, and the second devolatilization reactor is a horizontal double-shaft devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum system. The temperature of the first devolatilization reactor is 250 °C, and the reaction pressure is 2000 Pa. The temperature of the second devolatilization reactor is 260 °C, and the reaction pressure is 60 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.45, a monomer content of 0.02wt%, a cyclic oligomer content of 0.63wt% (of which the cyclic dimer content is 0.05wt%), and a hot water extractable content of 0.19wt% is obtained;

[0074] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 280 °C, and the winding speed is 4200 m / min. A high-quality polyamide 6 fine denier fiber is obtained, the fiber specification is 20D / 24F, the fiber breaking strength is 4.5 cN / dtex, and the elongation is 25%.

[0075] Example 4

[0076] A method for preparing a polyamide 6 fine denier fiber by anionic polymerization, the specific steps are as follows:

[0077] (1) Preparation of base active material A: 0.7 parts of NaH is added to 100 parts of caprolactam and mixed uniformly, then distilled under reduced pressure at 120 °C and 10 kPa to remove water, and then stored in a storage tank A under N2 protection and at a constant temperature of 130 °C;

[0078] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, distilled under reduced pressure at 120 °C and 10 kPa to remove water, then 1.7 parts of N-acetyl caprolactam (AcCL) and 0.9 parts of lanthanum aminocaproate are added and mixed uniformly, and then stored in a storage tank B under N2 protection and at a constant temperature of 130 °C;

[0079] (3) The base active materials A and B are injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization, the feeding temperature of the screw extruder is set to 130 °C, the discharging temperature of the screw extruder is set to 230 °C, the intermediate temperature of the screw is set to gradually increase from 130 °C to 230 °C, there are 5 heating sections, and the rotation speed is 50 rpm. A polyamide 6 base melt with a relative viscosity of 2.54, a monomer content of 3.59wt%, a cyclic oligomer content of 1.33wt% (of which the cyclic dimer content is 0.47wt%), and a hot water extractable content of 3.69wt% is prepared by reaction extrusion;

[0080] (4) The above base melt is transported through a pipeline to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a vertical falling-film devolatilization reactor, and the second devolatilization reactor is a vertical falling-film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum system. The temperature of the first devolatilization reactor is 280 °C, and the reaction pressure is 1000 Pa. The temperature of the second devolatilization reactor is 250 °C, and the reaction pressure is 40 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.56, a monomer content of 0.04wt%, a cyclic oligomer content of 0.77wt% (of which the cyclic dimer content is 0.02wt%), and a hot water extractable content of 0.21wt% is obtained;

[0081] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 280 °C, and the winding speed is 4500 m / min. A high-quality polyamide 6 fine denier fiber is obtained, the fiber specification is 70D / 136F, the fiber breaking strength is 4.8 cN / dtex, and the elongation is 24%.

[0082] Example 5

[0083] A method for preparing a polyamide 6 fine denier fiber by anionic polymerization, the specific steps are as follows:

[0084] (1) Preparation of base active material A: 0.9 parts of NaOH is added to 100 parts of caprolactam and mixed uniformly, then distilled to remove water at 130 °C and 30 kPa under reduced pressure, and then stored in a storage tank A under Ar protection and at a constant temperature of 120 °C;

[0085] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, distilled to remove water at 130 °C and 30 kPa under reduced pressure, then 1.4 parts of m-terephthalyl bis-caprolactam and 0.5 parts of magnesium nitrate are added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 120 °C;

[0086] (3) The base active materials A and B are injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization, the feeding temperature of the screw extruder is set to 160 °C, the discharging temperature of the screw extruder is set to 240 °C, the intermediate temperature of the screw is set to gradually increase from 160 °C to 240 °C, there are 5 heating sections, and the rotation speed is 60 rpm. A polyamide 6 base melt with a relative viscosity of 2.92, a monomer content of 3.57wt%, a cyclic oligomer content of 1.43wt% (of which the cyclic dimer content is 0.36wt%), and a hot water extractable content of 3.82wt% is prepared by reaction extrusion;

[0087] (4) The above base melt is transported to two series-connected devolatilization reactors through a pipeline, wherein the first devolatilization reactor is a vertical falling film devolatilization reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum system. The temperature of the first devolatilization reactor is 260 °C, and the reaction pressure is 1000 Pa, the temperature of the second devolatilization reactor is 260 °C, and the reaction pressure is 50 Pa, and finally a high-quality polyamide 6 melt with a relative viscosity of 2.93, a monomer content of 0.01wt%, a cyclic oligomer content of 0.73wt% (of which the cyclic dimer content is 0.06wt%), and a hot water extractable content of 0.23wt% is prepared;

[0088] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 285 °C, and the winding speed is 3000 m / min, and a high-quality polyamide 6 fine denier fiber is obtained, the fiber specification is 50D / 96F, the fiber breaking strength is 6.2 cN / dtex, and the elongation is 22%.

[0089] The polyamide 6 base melt, polyamide 6 final polymer and polyamide 6 fiber of the comparative example and examples 1 to 5 are subjected to performance characterization, and the performance characterization table is shown in Table 1 as follows:

[0090] Table 1 Performance characterization table of the polyamide 6 base melt, polyamide 6 final polymer and polyamide 6 fine denier fiber of the comparative example and examples 1 to 5

[0091]

[0092] It should be understood by those skilled in the art that the technical features of the above examples can be combined arbitrarily, and in order to make the description concise, all possible combinations of the technical features in the above examples are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present disclosure.

Claims

1. A method for preparing polyamide 6 fine denier fibers by anionic polymerization, comprising the following steps: (1) Prepare basic active material A: Mix the catalyst with caprolactam evenly to obtain the first mixture. After vacuum distillation of the first mixture, store it in storage tank A. Storage tank A is protected by an inert atmosphere and the temperature is constant at 80~150℃. (2) Preparation of basic active material B: After heating and melting caprolactam, perform vacuum distillation. Mix the caprolactam after removing water with the initiator and the cyclic oligomer inhibitor to obtain a second mixture. Store the second mixture in storage tank B, which is protected by an inert atmosphere and kept at a constant temperature of 80~150℃. The cyclic oligomer inhibitor is a metal ion compound MY or a mixture of two or more metal ion compounds MY, wherein M is Zn 2+ La 3+ Mg 2+ Y can be an inorganic or organic anion; (3) The basic active materials A and B components are injected into the screw extruder at a volume ratio of 1~10:10 for anionic polymerization and reactive extrusion to obtain polyamide 6 basic melt; (4) The polyamide 6 base melt is fed to the first devolatilization reactor to remove caprolactam monomer to obtain polyamide 6 intermediate. The polyamide 6 intermediate is fed into the second devolatilization reactor to remove a small amount of caprolactam monomer, cyclic dimer, part of cyclic trimer and part of cyclic tetramer to obtain polyamide 6 final polymer. The reaction temperature of the first devolatilization reactor is set to 240~280°C and the reaction pressure is 200~4000 Pa. The reaction temperature of the second devolatilization reactor is 240~280°C and the reaction pressure is 20~600 Pa. The first devolatilization reactor is selected from one of the following: horizontal cage reactor, horizontal disc reactor, strip devolatilizer and vertical falling film devolatilization reactor. The second devolatilization reactor is a vertical falling film devolatilization reactor or a horizontal biaxial devolatilization reactor. (5) The polyamide 6 final polymer is fed to a spinning machine for direct spinning to obtain polyamide 6 fine denier fibers.

2. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (1), the catalyst is one or more of sodium caprolactam, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, and KOH.

3. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that, In step (2), the initiator is one or more of N-acetylcaprolactam, bisacylcaprolactam-1,6-caprolactam, terephthaloyl biscaprolactam, isophthaloyl biscaprolactam, toluene diisocyanate, diphenylmethane diisocyanate, and 1,6-hexane diisocyanate.

4. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that, The conditions for vacuum distillation in steps (1) and (2) are a temperature of 80~150℃ and an absolute reaction pressure of 5~95kPa.

5. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (2), the inorganic or organic anion Y is selected from F. - Cl - NO3 - SO4 2- PO4 3- Citrate ion, salicylate ion, 3-hydroxybutyrate ion, lactate ion, malate ion, organic monocarboxylic acid ion H(CH2). n COO - Where n=0~12, benzoate ion, naphthoate ion, organic dicarboxylic acid ion COO - (CH2) m COO - Where m=0~12, unsaturated fatty acid ions, 6-aminohexanoate ions NH2C5H 10 COO - One of the amino acid anions; when the inorganic or organic anion is an unsaturated fatty acid anion, the unsaturated fatty acid anion is an oleate anion (C). 17 H 33 COO - Linoleate ion C 17 H 31 COO - α-Linolenic acid ion C 17 H 29 COO - Arachidonic acid ion C 19 H 31 COO - Palmitate ion C 15 H 29 COO - When the inorganic or organic anion is an amino acid ion, the amino acid ion is any one of glycine ion, alanine ion, valine ion, leucine ion, isoleucine ion, proline ion, phenylalanine ion, methionine ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteine ​​ion, tyrosine ion, and selenocysteine ​​ion, and the amount of cyclic oligomer inhibitor added is 0.01wt% to 2.0wt% of caprolactam.

6. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (3), the feed temperature of the screw extruder is set to 90~160℃, the discharge temperature is set to 220~240℃, the temperature of the middle section of the screw is set to gradually increase from the feed temperature to the discharge temperature, with no less than one heating section, and the rotation speed is 20~300rpm.

7. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (3), the relative viscosity of the polyamide 6 base melt is 2.0~3.5, the monomer content is less than 3.9 wt%, the cyclic oligomer content is less than 2.0 wt%, and the cyclic dimer content in the cyclic oligomer is less than 0.5 wt% and the hot water extractable content is less than 4.6 wt%.

8. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (4), the reaction temperatures of the first devolatilization reactor and the second devolatilization reactor can be controlled independently, and both are connected to a vacuum system. The vacuum system is used to control the reaction pressure of the first devolatilization reactor and the second devolatilization reactor.

9. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (4), the relative viscosity of the polyamide 6 final polymer is 2.0~3.5, the monomer content is less than 0.1wt%, and the cyclic oligomer content is less than 1.2wt%, wherein the cyclic dimer content in the cyclic oligomer is less than 0.1wt% and the hot water extractable content is less than 0.4wt%.

10. The method for preparing polyamide 6 fine denier fibers by anionic polymerization according to claim 1, characterized in that... In step (5), the spinning temperature is 245~300 °C and the spinning speed is 2500~6000 m / min.

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